Aspirin Therapy: Are You Reaping Its Benefit?

If you have risk factors for a heart attack, you may be popping a daily aspirin. But do you know why and whether you are getting its full protective effect?

Aspirin protects against heart attacks and strokes by preventing clumping, called aggregation, of blood platelets, which in turn can lead to an artery-blocking blood clot. But even though millions of people in the United States take a daily aspirin to get this protection, most are not aware that their bodies may be resistant to the anti-clumping effects of aspirin.

Aspirin therapy usually consists of one adult aspirin (325 mg) daily or every other day, or one "baby" aspirin (81 mg) daily. It's not clear which one is the most effective dose, especially in people who are resistant to its action.

One study done about 15 years ago found that some patients treated to prevent a second stroke required large doses of aspirin to attain complete blockage of platelet aggregation. About 3 percent of them did not respond fully even when given 1,300 mg of aspirin daily.

And here's another twist: People with type 2 diabetes may be more likely to have aspirin resistance, according to a recent small study of patients with heart disease and diabetes. A small aspirin dose (81 mg) was associated with resistance in as many as 37 percent of those with diabetes and 14 percent of those without diabetes.

At the highest aspirin dose (325 mg), platelet aggregation was the same, regardless of whether they had diabetes. Even at the highest dose, however, about one-sixth of the people in both groups were not able to fully stop platelet aggregation. The authors of this study emphasize the need for further evaluation of the effects of diabetes on aspirin resistance.

Earlier studies showed that women and older individuals are also more likely to be resistant to the anti-clumping effects of aspirin.

How can you find out if you are among those who are resistant to this action of aspirin? Tests are available to measure the response of your platelets to aspirin, and some centers are promoting such tests.

But an expert researcher on aspirin resistance here at Johns Hopkins told me he does not believe these tests are reliable. Another possible solution is to take the higher dose of aspirin (325 mg daily), recognizing that higher doses are associated with a greater risk of dangerous bleeding.

The American Gastroenterology Association recommends screening for Helicobacter pylori infections of the stomach, the major cause of stomach ulcers, for all people at high risk for gastrointestinal complications before starting therapy with aspirin or any other nonsteroidal anti-inflammatory drug (NSAID).

My suggestion is that people with diabetes, especially those at high risk for a heart attack or stroke, take a dose of 325 mg of aspirin rather than a smaller dose, but that they should first talk with their doctors about balancing their danger of gastrointestinal bleeding against their lowered risk of a heart attack or stroke.

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